Exhaust gas heat exchanger

ABSTRACT

The invention relates to an exhaust gas heat exchanger ( 2 ) comprising a bundle of pipes ( 21 ) consisting of exhaust gas pipes ( 22 ) and a bypass channel ( 23 ) in a common housing. The pipe bundle is arranged in a first chamber that is crossflown by a liquid coolant and the bypass channel is arranged in a second, separate chamber. The pipe bundle and the bypass channel lead into a common exhaust gas inlet area and a common exhaust gas outlet area in which an exhaust gas valve actuated by a servo-drive is arranged, said valve guiding the exhaust gas flow through the pipe bundle or the bypass channel. According to the invention, the exhaust gas valve has a movable closing organ that is resistant to bending, said organ being preferably embodied as a pivoting semi-flap ( 27 ) that is fixed with a longitudinal side ( 28 ) to a drive shaft ( 30 ) that is arranged crosswise relative to the exhaust gas flow (A).

The invention relates to an exhaust gas heat exchanger in accordancewith the preamble of patent claim 1, as has been disclosed by DE-A 19962 863 in the name of the present Applicant.

In this known exhaust gas heat exchanger, a bypass passage is integratedtogether with the exhaust gas heat exchanger in a housing. The actualexhaust gas heat exchanger comprises a bundle of exhaust gas tubes whichare rectangular in cross section and are arranged in a heat exchangerhousing through which the coolant of the coolant circuit of an internalcombustion engine flows. Therefore, the heat of the exhaust gases passesinto the coolant circuit of the internal combustion engine via thecoolant and therefore also into the heating circuit, in which a radiatorthrough which the coolant flows is arranged. The heating of the coolantcircuit by means of the exhaust gas heat also allows the vehicleinterior compartment to be heated more quickly. This exhaust gas heatexchanger therefore functions as an additional heating means in thewarming-up phase. Should heating of the coolant circuit be undesirable,the exhaust gas stream, in the known exhaust gas heat exchanger, ispassed through a bypass passage which is thermally insulated from theexhaust gas tubes and the coolant. Consequently, the exhaust gas streamflowing through the bypass passage releases scarcely any heat to thecoolant. The exhaust gas stream is made to pass through the exhaust gastubes around which the coolant flows or through the insulated bypasspassage via an exhaust gas valve which is arranged either in the exhaustgas inlet region or in the exhaust gas outlet region and is actuated byan actuating drive. In the known exhaust gas heat exchanger, the exhaustgas valve is designed as an elastic, flexible diverter member.

Exhaust gas heat exchangers are also used as what are known as exhaustgas coolers in the exhaust gas recirculation system in motor vehicles,in particular those having diesel engines. EP-A 987 427 has disclosed anexhaust gas cooler of this type, installed in an exhaust gasrecirculation (EGR) system. This exhaust gas cooler has a heat exchangerwith exhaust gas tubes that are U-shaped in form, i.e. the inlet andoutlet cross sections for the exhaust gas tubes lie at the same end ofthe exhaust gas cooler and are separated from one another by apartition. This inlet and outlet end of the exhaust gas cooler isassigned a valve device with a shut-off valve and a bypass passage. Thisenables the exhaust gas stream either to be passed through the exhaustgas cooler, so that the exhaust gas is cooled by the coolant, or to beblocked from flowing to the exhaust gas cooler, so that the exhaust gasstream is passed through the bypass passage—in this case the exhaust gasis not cooled. The bypass passage forms part of the valve device and notpart of the exhaust gas cooler.

It is an object of the present invention to improve an exhaust gas heatexchanger of the type described in the introduction in such a way thatsimple, operationally reliable switching of the exhaust gas streambetween on the one hand the heat transfer part and on the other hand thebypass passage is possible.

For the heat exchanger of the generic type, this object is achieved bythe characterizing features of patent claim 1. According to thesefeatures, the exhaust gas valve for controlling the exhaust gas streamhas a rigid closure member which is matched to the thermal, mechanicaland dynamic loads of an exhaust gas heat exchanger.

According to an advantageous refinement of the invention, the closuremember is designed as what is described as a half-flap, i.e. a flapwhich is secured on one longitudinal side, with the pivot pin lying inthe center of the cross section of flow and the half-flap in each caseclosing off and leaving open half the cross section of flow, i.e. eitherthe bypass passage cross section or the heat exchanger cross section.This half-flap is simple to actuate from the outside via a drive shaftand in the closed position bears against the inner wall of the exhaustpipe on the circumferential side. In its closed position, the half-flapadvantageously adopts a position running obliquely with respect to theexhaust gas direction of flow and is pressed onto the inner housing wallof the discharge passage by the exhaust gas pressure. This allows astable closed position to be produced.

According to an advantageous refinement of the invention, a partition isprovided between pivot pin and inlet cross section of the exhaust gasheat exchanger, which results in improved sealing with respect to thediverted exhaust gas stream.

According to an advantageous refinement of the invention, the closuremember is designed as a pivot flap with an approximately centrallyarranged pivot pin. The downstream sealing edge of the pivot flap slidesalong a sealing surface which is concave or cylindrical in design and issecured upstream of the inlet cross sections of the exhaust gas tubebundle and the bypass passage by means of a partition. On account of thecentral arrangement of the pivot pin, the actuating forces required topivot this flap are lower; the pivot flap is pressure-compensated aboutthe axis of rotation, i.e. the static pressure does not produce anyrotation of the flap. In an advantageous refinement of this embodiment,the exhaust gas flow passage is widened in the pivot region in such amanner that diverting zones for the exhaust gas are formed. This avoidsan excessively high pressure loss. An eccentric arrangement of the pivotpin may also be advantageous: this allows the downstream pivot range ofthe sealing edge and therefore the size of the sealing surface to bereduced.

According to an advantageous refinement of the invention, the closuremember is designed as a pivot flap with closure surfaces arrangedapproximately at right angles to one another, with the pivot pin beingarranged approximately at the intersection point of the closuresurfaces. This simple flap geometry enables either the tube bundle orthe bypass passage to be closed off by one of the two closure surfacesby means of a pivoting movement of 90°, while the other closure surfaceis oriented in the direction of flow of the exhaust gas and thereforegenerates scarcely any resistance. A stable closure position is ensuredby the pressure of the exhaust gas stream acting on the closure surfacelocated transversely thereto. This design as an angle flap results in ashort overall length.

According to an advantageous refinement of the invention, the closuremember is designed as a plate slide which can move transversely withrespect to the exhaust gas flow and has a cross-sectional area which isapproximately half the total cross section of flow. As a result, in eachcase half of the cross section can be blocked off by a simpletranslational movement, which is preferably initiated by means of avacuum cell. It is advantageous for this plate slide to be accommodatedin a sliding manner in lateral guide grooves. This plate slide may bearranged in either the exhaust gas inlet region or the exhaust gasoutlet region. This plate slide is particularly simple to drive, sincethere is no need for linkages or crank elements, as are required for apivoting motion. This design as a plate slide makes the overall lengthextremely short.

According to an advantageous configuration of the invention, each of theabovementioned closure members can be driven by means of a vacuum cellwhich is arranged outside the valve housing and is in widespread use asan actuating drive in particular in motor vehicles. The translationalmovement of the vacuum cell can be converted into a pivoting movement bymeans of a simple linkage.

According to an advantageous refinement of the invention, theabovementioned exhaust gas heat exchanger may particularlyadvantageously be used as an exhaust gas cooler in an exhaust gasrecirculation system (EGR system) for motor vehicles, in particular withdiesel engines or direct injection spark ignition engines. The use ofthis exhaust gas heat exchanger with an integrated bypass results invery favorable installation and assembly conditions, since the exhaustgas heat exchanger—partly on account of its rectangular crosssection—can be arranged relatively close to the engine block, in aspace-saving manner, without the need to produce and fit an additionalbypass tube.

Exemplary embodiments of the invention are illustrated in the drawingand described in more detail in the text which follows. In the drawing:

FIG. 1 shows an exhaust gas recirculation system with exhaust gas coolerand integrated bypass,

FIG. 2 shows a perspective view of the inlet cross section of theexhaust gas cooler,

FIG. 3 shows a perspective view of the exhaust gas cooler with exhaustgas valve and half-flap,

FIG. 4, 4 a show a second embodiment of the exhaust gas valve with pivotflap,

FIG. 5, 5 a show a third embodiment of the exhaust gas valve, with angleflap, and

FIG. 6, 6 a, 6 b show a fourth embodiment of the exhaust gas valve, as aplate slide.

FIG. 1 diagrammatically depicts an exhaust gas recirculation system (EGRsystem) having the individual components arranged in the intake air orexhaust gas circuit. The ambient air, represented by an arrow 1, issucked in via a turbo-compressor 2, which for its part is driven by anexhaust gas turbine 3. The compressed and heated intake air passes via aline 4 into the charge air cooler 5, where it is cooled, and from therevia a line 6 to the intake section of a diesel engine or a directinjection spark ignition engine 7. The air which is burnt in the engineemerges via the pipe 8 from the engine 7 into the pipe 8 as exhaust gasvia the exhaust section and then passes into the exhaust gas turbine 3and from there into the open air. In the exhaust section 8, exhaust gasis branched off at a branch point 9 and fed back into the intake airpassage 6 in a loop 10 via an exhaust gas recirculation valve 11. TheEGR valve 11 controls the quantity of exhaust gas that is recirculated.An exhaust gas cooler 12 with an integrated bypass 13, which has theexhaust gas flowing through it on the primary side and is cooled on thesecondary side by the coolant branched off from the coolant circuit (notshown) of the engine 7, is arranged in the loop 10. Upstream of theexhaust gas cooler 12, as seen in the exhaust gas direction of flow,there is an exhaust gas valve 14, which functions as a points system andpasses the exhaust gas stream either through the exhaust gas cooler 12in order to be cooled or through the bypass 13 if cooling of the exhaustgas is not required. This exhaust gas recirculation allows theconsumption and emission levels in the engine 7 to be reduced—thisexhaust gas recirculation procedure forms part of the known prior art.The following figures describe exemplary embodiments in which theexhaust gas cooler 12, the bypass 13 and the exhaust gas valve 14 areintegrated to form a single structural unit.

FIG. 2 shows a perspective illustration of the inlet cross section of anexhaust gas cooler 20, which includes firstly a tube bundle 21 composedof six exhaust gas tubes 22 which are rectangular in cross section, andsecondly a bypass passage 23, with the cross sections of flow of thetube bundle 21 and the bypass passage 23 being approximately identical.As is known per se and consequently not illustrated here, the coolant ofthe cooling circuit flows around the exhaust gas tubes 22, i.e. theexhaust gas flowing through the exhaust gas tubes 22 dissipates its heatto the coolant in the coolant circuit of the engine.

FIG. 3 shows the exhaust gas cooler 20 described in FIG. 2, likewise inthe form of a perspective illustration, with an upstream exhaust gasvalve 24 which has a housing 25 with an inlet connection piece 26 and iswelded to the exhaust gas cooler 20. In the interior of the housing 25there is what is described as a half-flap 27, which is approximatelyrectangular in cross section, specifically having a longitudinal edge 28and an outer sealing edge 29. The inner longitudinal edge 28 is securedto a drive shaft 30, which for its part is mounted in a rotatable butaxially fixed position in two bearings 31 and 32 located outside thehousing 25 and is sealed with respect to the outside. The exhaust gasenters the valve housing 24 through the inlet connection piece 26 in thedirection indicated by the arrow A. A partition 33 is arranged beneaththe drive shaft 30 in the direction flow; this partition isapproximately rectangular in cross section and has an upper longitudinaledge 34 adjoining the drive shaft 30, while a lower longitudinal edge 35is arranged in a sealing manner between the inlet cross sections,illustrated in FIG. 2 of the tube bundle 21 and the bypass passage 23.The drive shaft 30 and therefore the half-flap 27 are driven by anactuating element, of which in the present figure only an output elementin the form of a crank disk 36 is illustrated. In the position of thehalf-flap 27 illustrated in FIG. 3, therefore, the lower cross sectionof the exhaust gas cooler, i.e. according to the illustration shown inFIG. 2 the bypass passage 23, is covered, so that the entire exhaust gasstream A flows through the upper cross section of the exhaust gas cooler20, i.e. through the tube bundle 21. As a result, the exhaust gas iscooled. As can be seen from the illustration presented in FIG. 3, thehalf-flap 27 is arranged obliquely with respect to the direction of flowof the exhaust gas—this firstly results in a reduced pressure loss forthe exhaust gas flow and secondly results in a sufficient pressingaction on the half-flap to increase the sealing action.

FIG. 4 shows a further embodiment of an exhaust gas valve 40, which hasa pivot flap 41 with two sealing edges 42 and 43 and a centrallyarranged pivot pin 44. This exhaust gas valve 40 is connected upstreamof the exhaust gas cooler 20 (same reference numerals as in FIG. 2)comprising the exhaust gas tubes 22 and the bypass passage 23 and isconnected to the exhaust gas cooler to form a single structural unit. Apartition 45, which at its upstream end has a concave, cylindricalsealing surface 46, is arranged between the inlet cross section 22 a forthe exhaust gas tubes 22 and the inlet cross section 23 a for the bypasspassage. This sealing surface 46 interacts with the sealing edge 43 ofthe pivot flap 41 and, in terms of the length of the arc, extends overthe pivot range of the flap 41. On account of this design of the sealingsurface 46, the housing of the exhaust gas valve 40 has a widened crosssection in this region, with widened sections 47 and 48, so that theexhaust gas stream is provided with a sufficient cross section to passthrough and is therefore not subject to an excessively high pressuredrop.

As a modification to the illustration presented in FIG. 4, the pivot pinmay also be arranged eccentrically, so that the flap part-surfaces areof different sizes on either side of the pivot pin, resulting, with thesame pivot angle, in a shorter concave sealing surface the closer thepivot pin moves toward the sealing surface.

FIG. 4 a shows the driving of the pivot flap 41 by means of a vacuumcell 49, the structure and function of which are known per se. Thisvacuum cell 49 is secured to the outer side of the exhaust gas valve 40and has a piston rod 50 which is articulatedly coupled to a driver disk51. The driver disk 51 is secured, in a manner fixed in terms ofrotation, to a drive shaft 52 which adjusts the pivot flap 41. In thisway, the translational movement of the piston rod 50 and the eccentricarticulation by means of the driver disk 51 produce a rotary motion forthe pivot flap 41; a pivot range of approximately 60° is sufficient toopen up either the upper or the lower cross section of the exhaust gascooler.

FIG. 5 shows a further embodiment with an exhaust gas valve 60 which isconnected upstream of the exhaust gas cooler 20 (which once again usesthe same reference numerals as above). Immediately upstream of the inletcross section of the exhaust gas tubes 22 and the bypass passage 23there is what is known as an angle flap 61, which has two closuresurfaces 62 and 63 which are arranged approximately at right angles toone another and the cross sections of which are dimensioned in such away that they respectively cover the inlet cross section of the exhaustgas tubes 22 or of the bypass passage 23. The angle flap 61 can bepivoted, approximately through 90°, about a pivot pin 64 arrangedapproximately at the apex of the two closure surfaces 62 and 63. In thepivot position of the flap 61 which is illustrated, therefore, theclosure surface 62 is closing off the exhaust gas tubes 22, so that thebypass passage 23 is open; in this position, the second closure surface63 extends in the direction of the exhaust gas stream A, i.e. itpresents only a minimal resistance to the exhaust gas stream, whereasthe other closure surface 62 is pressed onto the inlet cross section ofthe tubes 22 by the exhaust gas stream. This results in a stable closureposition.

FIG. 5 a shows the driving of the angle flap 61, once again produced bymeans of a vacuum cell 65, which via its piston rod 66 and a driver disk67 articulatedly connected thereto drives the drive shaft 64, i.e.imparts a pivoting movement of 90° to it.

FIG. 6 shows a further exemplary embodiment of an exhaust gas valve 60,which this time is connected downstream of the exhaust gas cooler 20(for which the same reference numerals are used once again)—thedirection of flow of the exhaust gas is indicated by the arrows A. Theexhaust gas valve 70 has a housing 71 which is approximately rectangularin cross section, matched to the cross section of the exhaust gas cooler20. Guide grooves 72 and 73 are secured to the housing 71 on the twonarrow sides 71 a, 71 b of the housing 71; these guide grooves extendover the entire height of the cross section of flow and receive thelongitudinal edges 74 a, 74 b of a plate slide 74, the cross-sectionalarea of which corresponds to approximately half the cross-sectional areaof the valve housing 71 or of the exhaust gas cooler 20. An actuatingrod 75, which is connected to the piston of a vacuum cell 76 in a mannernot illustrated in more detail, is secured to the plate slide 74. Sincethe piston (not shown) of the vacuum cell 76 executes a translationalmovement, in this case there is no need for any transmission means forconverting such a movement into a rotary movement, but rather theactuating piston of the vacuum cell is directly coupled to the actuatingrod 75 of the slide 64. This results in a particularly simple drivemechanism. In the exemplary embodiment illustrated, the slide 74 isarranged downstream of the exhaust gas cooler 20, although it is alsoentirely possible for it to be arranged upstream.

1. An exhaust gas heat exchanger comprising: a tube bundle composed ofexhaust-gas tubes, a bypass passage in a common housing, and an exhaustgas valve comprising a flexurally rigid, moveable closure member,wherein the tube bundle is arranged in a first space, through whichliquid coolant flows, and the bypass passage is arranged in a second,separate space, wherein the tube bundle and the bypass passage open intoa common exhaust gas inlet region and a common exhaust gas outletregion, wherein the exhaust gas valve is arranged in the inlet regionand is actuated by an actuating drive and guides the flow of exhaust gasthrough the tube bundle or the bypass passage, wherein the closuremember is designed as a pivotable half-flap, one longitudinal side ofwhich is secured to a drive shaft arranged transversely with respect tothe exhaust gas flow (A), and wherein the half-flap is arranged in avalve housing with an approximately rectangular cross section of flowand alternately closes off one half of the cross section or the otherhalf of the cross section.
 2. The exhaust gas heat exchanger as claimedin claim 1, wherein a partition is arranged between the drive shaft andthe inlet cross sections of the tube bundle and the bypass passage. 3.The exhaust gas heat exchanger as claimed in claim 1, wherein thehalf-flap closes in the exhaust gas direction of flow (A) and in theclosed position is arranged obliquely with respect to the exhaust gasstream (A).
 4. The exhaust gas heat exchanger as claimed in claim 1,wherein the actuating drive comprises vacuum cell, an actuating memberof which drives the closure member.
 5. An exhaust gas recirculationsystem comprising an exhaust gas heat exchanger according to claim
 1. 6.A motor vehicle comprising a heat exchanger according to claim
 1. 7. Anexhaust gas heat exchanger comprising: a tube bundle composed ofexhaust-gas tubes, a bypass passage in a common housing, and an exhaustgas valve comprising a flexurally rigid, moveable closure member,wherein the tube bundle is arranged in a first space, through whichliquid coolant flows, and the bypass passage is arranged in a second,separate space, wherein the tube bundle and the bypass passage open intoa common exhaust gas inlet region and a common exhaust gas outletregion, wherein the exhaust gas valve is arranged in the inlet regionand is actuated by an actuating drive and guides the flow of exhaust gasthrough the tube bundle or the bypass passage, wherein the closuremember is designed as a pivot flap with an approximately centrallyarranged pivot axle and two opposite sealing edges, wherein a partitionwith a concave sealing surface facing the pivot flap is arranged betweenthe pivot axle and the inlet cross sections of the tube bundle and ofthe bypass passage, and wherein the downstream sealing edge slides alongthe sealing surface over the pivoting range.
 8. The exhaust gas heatexchanger as claimed in claim 7, wherein the pivot flap is arranged in ahousing, the cross section of flow of which widens downstream of thepivot axle, to form flow-diverting regions.
 9. The exhaust gas heatexchanger as claimed in claim 7, wherein the actuating drive comprises avacuum cell, an actuating member of which drives the closure member. 10.An exhaust gas recirculation system comprising an exhaust gas heatexchanger according to claim
 7. 11. A motor vehicle comprising a heatexchanger according to claim
 7. 12. An exhaust gas heat exchangercomprising: a tube bundle composed of exhaust-gas tubes, a bypasspassage in a common housing, and an exhaust gas valve comprising aflexurally rigid, moveable closure member, wherein the tube bundle isarranged in a first space, through which liquid coolant flows, and thebypass passage is arranged in a second, separate space, wherein the tubebundle and the bypass passage open into a common exhaust gas inletregion and a common exhaust gas outlet region, wherein the exhaust gasvalve is arranged in the inlet region and is actuated by an actuatingdrive and guides the flow of exhaust gas through the tube bundle or thebypass passage, wherein the closure member is designed as an angle flapwith two limbs fixedly arranged approximately at right angles to oneanother and having a common apex, at which the closure member is mountedfor rotation about a pivot axle, and wherein one limb selectively pivotsabout the pivot axle to respectively cover an inlet cross section of thetube bundle or the bypass passage while the other limb is orientedparallel to the exhaust gas flow (A).
 13. The exhaust gas heat exchangeras claimed in claim 12, wherein the actuating drive comprises a vacuumcell, an actuating member of which drives the closure member.
 14. Anexhaust gas recirculation system comprising an exhaust gas heatexchanger according to claim
 12. 15. A motor vehicle comprising a heatexchanger according to claim
 12. 16. An exhaust gas heat exchangercomprising: a tube bundle composed of exhaust-gas tubes, a bypasspassage in a common housing, and an exhaust gas valve comprising aflexurally rigid, moveable closure member, wherein the tube bundle isarranged in a first space, through which liquid coolant flows, and thebypass passage is arranged in a second, separate space, wherein the tubebundle and the bypass passage open into a common exhaust gas inletregion and a common exhaust gas outlet region, wherein the exhaust gasvalve is arranged in the inlet region and is actuated by an actuatingdrive and guides the flow of exhaust gas through the tube bundle or thebypass passage, wherein the closure member is designed as a plate slidethat can move transversely with respect to the exhaust gas direction offlow (A) and has a cross-sectional area which approximately correspondsto half the cross section of flow.
 17. The exhaust gas heat exchanger asclaimed in claim 16, wherein the plate slide is arranged immediatelyupstream of the inlet cross sections or downstream of the outlet crosssections of the exhaust gas cooler and has two parallel longitudinaledges which are arranged slideably in housing-side guide grooves. 18.The exhaust gas heat exchanger as claimed in claim 16, wherein anactuating rod which is connected to the actuating drive is secured tothe plate slide.
 19. The exhaust gas heat exchanger as claimed in claim16, wherein the actuating drive comprises a vacuum cell, an actuatingmember of which drives the closure member.
 20. An exhaust gasrecirculation system comprising an exhaust gas heat exchanger accordingto claim
 16. 21. A motor vehicle comprising a heat exchanger accordingto claim 16.